Synthetic polycyclic musks are used extensively as fragrances and are released ubiquitously in our environment, particularly water. We have demonstrated that these compounds display very weak oestrogenic activity in vitro, although no obvious oestrogenic activity was found in young rats or zebrafish. We demonstrated, however, that the oestrogenic effect of these compounds is cell- and oestrogen receptor-type specific, raising the possibility that the in vivo models may have underestimated some effects. In addition, polycyclic musks were found to possess antioestrogenic (ERbeta-selective), antiandrogenic and antiprogestagenic activity. As recent research clearly demonstrates the possibility of endocrine disrupting environmental compounds to act in concert, more research to these combined effects is important. We have developed efficient methods to measure such combined bioactivities in a range of matrices using human cell-based reporter gene assays. So far, we found agonistic, rather than antagonistic, effects in water samples, suggesting a predominance of agonistic compounds in such samples.